Bog Shamans are a crucial part of the Swamp Orcs faction. They are your primary boost generation, which can be used for Emerge, Regenerate, and most importantly, Mugglug and her attacks. However, they can’t be used for Vinemancers and Bog Witches.
To be competitive, you need to try to keep at least 1 or 2 Shamans alive on-board most of the time. They have decent stats for the cost and can provide ranged support to finish low life units. With their 3 life for 1 cost, they can take a hit in a pinch and maybe provide some protection to a more critical unit in the moment. So while you need 1 or 2 on-board, if you have more, don’t be afraid to use them in the front line to absorb hits and finish enemy units.